The invention relates to a cathode arrangement for an x-ray tube comprising a cathode cup for electron focusing which exhibits a groove-like cavity for the heater coil.
In the case of cathode arrangements of this type, it is known to influence the size of the focal spot by changing the potential of the cathode cup or by changing the position of the heater coil in the cathode cup. The deeper the heater coil lies in the groove-like cavity of the cathode cup, namely, the smaller the focal spot. However, through these measures, it is virtually only possible to influence the linear focal spot in its one direction; namely, in its smaller dimension. The other dimension; namely, the longitudinal dimension of the focal spot, can hardly be influenced in the case of the known x-ray tubes.